A so-called organic thin film electric field light-emitting device is such a device wherein excitation arises as a result of recombination of electrons and holes injected from a pair of electrodes, the resulting excitation emits light in the process of radial deactivation, and the light is radiated towards the outside through a transparent electrode and a glass substrate. In such an electric field light-emitting device, it is required that injection of carriers should be controlled towards the inside of the electric field light-emitting device.
A first conventional electric field light-emitting device is disclosed in the Japanese Patent Kokai No. 4-51494. In this electric field light-emitting device, the surface of a transparent electrode formed on a glass substrate is covered with an insulating film except for a portion for injecting carriers thereby to avoid unnecessary injection of the carriers. More specifically, after forming the transparent electrode, the whole surface of which is covered with the insulating film such as SiO2 film and the like in accordance with chemical vapor deposition (CVD) method or sputtering method, an aperture is defined on the insulating film by locally etching a portion corresponding to that for injecting carriers for light-emitting device in accordance with photolithographic process, and then an organic thin film (hole transportation layer and light-emitting layer) and a metal electrode are formed thereon.
A second conventional electric field light-emitting device is disclosed in the Japanese Patent Kokai N. 3-233891. In this electric field light-emitting device, a light-emitting layer is formed in an island-shape so as to separate from the other elements, respectively. The fabricating method therefor is such that a hole transportation layer is formed on a transparent electrode by means of vapor deposition method or the like, and thereafter a light-emitting layer is locally deposited to form the same by, for example, shadow mask method. Then, a metal electrode is formed by the use of another pattern mask in accordance with shadow mask method.
A third conventional electric field light-emitting device is disclosed in the Japanese Patent Kokai Nos. 4-19993 and 4-363896. In this electric field light-emitting device, a metal electrode is formed from a plurality of materials. A substrate metal electrode which has been prepared by utilizing a material and a process for providing good adhesion is disposed between the surface of an organic thin film composed of a hole transportation layer and a light-emitting layer and the metal electrode. The reason for disposing the substrate metal electrode is in improvements in adherent properties between the metal electrode and the organic thin film and in injection characteristic properties of carriers, so that the substrate metal electrode is formed on the whole surface of the underside of the metal electrode.
In the first to third conventional electric field light-emitting devices, however, there are disadvantages as explained below.
Although the first conventional electric field light-emitting device achieves an object for injecting carriers inside the electric field light-emitting device, it requires an expensive production facilities for CVD method (or sputtering method) and for photolithographic process, besides it utilizes expensive process steps (the number of steps is remarkable), so that this conventional electric field light-emitting device becomes expensive from economical point of view.
In the second conventional electric field light-emitting device, it is difficult to work the light-emitting layer so that stability in the fabrication process is deficient, besides since the light-emitting layer which is a major stage for light emission must be worked in a poor state of controllability, the device properties are also unstable.
In the third conventional electric field light-emitting device, although the two-layered metal electrodes are employed, since the upper and lower metal electrodes have an identical size with each other, electrons injected from an end of the electrodes spread to affect adjacent light-emitting devices, whereby there arises a problem of cross talk.